The present invention pertains to electric powered bucket cranes and hoists. More specifically, the present invention relates to methods and devices for controlling movement of a hoist bucket.
Hoist buckets are used on clam shell and grapple cranes to dig and move material from one location to another. The proper movement of such buckets requires the coordinated movement of two motors: one for raising and lowering the bucket and one for opening and closing the bucket. Proper coordination of the hoist motors is needed for these operations. For example, proper control is necessary so that the bucket will not unexpectedly open when it is being moved up or down due to slack in the hoist lines. To prevent this in the prior art, some designs have used a static stepless control using wound rotor motors. Another technique that has been used is providing the device with a Programmable Logic Controller (PLC) to separately control the speed of each hoist so that the load is shared equally. This solution is undesirable because the machine operators have difficulty operating the unit and it also adds cost and complexity.
Several U.S. Patents are directed to various types of controllers. These include U.S. Pat. No. 778,897, issued to Robb et al. on Jan. 3, 1905; U.S. Pat. No. 4,231,698, issued to Lado on Nov. 4, 1980; U.S. Pat. No. 5,392,935 Kazama et al. Feb. 28, 1995; U.S. Pat. No. 6,023,862 Sirjola Feb. 15, 2000; Japanese Patent No. JP1203194 Keiji Aug. 15, 1989; Japanese Patent No. JP4358695 Masao, et al. Dec. 11, 1992; and WTO Patent No. WO 98/06657 Sirjola Feb. 19, 1998.
U.S. Pat. No. 778,897 issued to Robb on Jan. 3, 1905 discloses a Motor Control for Hoisting Buckets. This patent shows a two cable control systems for hoisting buckets.
U.S. Pat. No. 4,231,698 issued to Lado on Nov. 4, 1980 discloses a system for one-hand control of two winches during hoisting of closed clamshell, with differentiation. This patent discloses the use of two operating control lines for controlling the opening, closing and hoisting of a bucket. This patent notes that the hydraulic winch for the closing line should be the one utilized to lift the bucket and the second line is just to be taken in to control slack. The control of slack in the second line is done by placing the second winch motor in tandem with the first motor such that the exhaust of the hydraulic fluid from the first motor travels through the second motor. The motor valves are then utilized to control the motors separately and control the back pressure from the first motor into the second motor.
U.S. Pat. No. 5,392,935 issued to Kazama et al. on Feb. 28, 1995 discloses a control system for cable crane. This patent discloses the use of an opening and closing gate operated by a hydraulic cylinder and a limit switch for detecting the opening and closing of the gate. This patent does not describe the use of two cable lines in order to control the opening and closing of the clamshell type bucket.
U.S. Pat. No. 6,023,862 issued to Sirjola on Feb. 15, 2000 discloses a control system for a rope bucket. This patent describes the use of a control system which includes a hoist mechanism for hoisting a rope bucket and a close mechanism for closing and opening the scoop of the rope bucket and also for hoisting and lowering the rope bucket. This invention is directed to the elimination of a transfer system and utilizes the same bucket support system for opening and closing of the bucket, lifting and lowering of the bucket, and transfer of the bucket horizontally.
Japanese Patent No. JP1203194 issued to Manabe Keiji on Aug. 15, 1989 discloses a hoist control method for crane provided with rope type bucket. This patent describes the operation of a controller for setting the output frequency of a supporting inverter so that the speed of a hoist and opening closing controlling motor are identical based upon the detected output frequency of the open close inverter during the hoist work.
Japanese Patent No. JP4358695 issued to Yamamoto Masao et al. on Dec. 11, 1992 discloses a clamp control for crane with rope type bucket. This patent describes the use of two motors with two inverter devices with variable voltage and variable frequency. It then describes the controlling of the speed of the D motors by the inverter devices to open the bucket, lower the open bucket and then close the bucket.
World Organization Patent No. WO 98/06657 is an international filing similar to U.S. Pat. No. 6,023,862 issued to Sirjola.
These patents fail to describe the advantages of the present invention described herein.
The novel control device of the present uses a programmable flux vector inverter to provide load sharing and speed matching control features required for a dual hoist bucket application such as a Clam-Shell or Grapple type crane application. The drive software of the present invention makes it possible to operate the hoist motions on a bucket crane without the need for a Programmable Logic Controller (PLC) or other external logic.
The use of this drive software makes it possible to operate hoist motions on a bucket crane without the need for a PLC or other external logic by utilizing load sharing and speed matching control features within the motor control system. This is done by utilizing speed and torque control modes for operating the motors and providing signals appropriate to the motors to maintain the motors in the same relative position and operating at the same relative speed.
The xe2x80x9choldxe2x80x9d and xe2x80x9cclosexe2x80x9d inverter drives are completely independent and do not need to xe2x80x9ccommunicatexe2x80x9d with one another such-as in a xe2x80x98masterxe2x80x99/xe2x80x98slavexe2x80x99 type arrangement where the master drive always controls the operation of the slave drive. Each hoist motion can be operated individually via a dual axis master switch. If either hoist is lowered/raised individually it will open/close the bucket accordingly. If both hoists are raised simultaneously the bucket will automatically try, to close due to the proportional load sharing. If both hoists are lowered simultaneously the bucket will remain in the operating condition (open or closed) it was in when it started the motion. This is due to the fact that both drives are in speed control mode when lowering. As long as the speed reference signals to both drives are identical the hoist motions will match speed in the lower direction.